Information reproducing apparatus and method

ABSTRACT

A pit data generation circuit generates a first clock signal synchronized with pit data and a pit synchronization signal from a sum read signal obtained by reading the length of a pit. A division circuit generates a second clock signal by frequency-dividing the first clock signal. The division circuit is reset by the pit synchronization signal, and is capable of adjusting the phase of the second clock signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for and a method ofreproducing information from an information recording medium, such as anoptical disc.

2. Description of the Related Art

In the optical disc represented by a Compact Disc (CD) and a DVD, thelong or short length of a pit is used to record information. However, inorder to record information for copy control for the prevention ofillegal copying or the like, there is a request for reserving anotherrecording area without decreasing a recording capacity by the pit.

As a method of increasing the recording capacity by other means exceptthe method using the long or short length of the pit, there is known atechnique of displacing or shifting the position of the pit in theradial direction of the optical disc. This technique is such thatinformation is recorded by wobbling the position of the pit in theradial direction of the optical disc and by performing spread spectrumwith respect to the wobble.

Such a method of reproducing the spread spectrum data from the opticaldisc is disclosed in Japanese Patent Application Laying Open NO.2003-85896. This technique is such that a clock signal is extracted froma read signal corresponding to the movement of a pit position aside froma read signal obtained by detecting the length of the pit, and that datais reproduced by using the extracted clock signal.

However, the structure of an information reproducing apparatus becomescomplicated if the clock signal is reproduced differently from the readsignal obtained by detecting the length of the pit. Also if the clocksignal is reproduced from the read signal corresponding to the movementof the pit position, it is influenced by the eccentricity of the opticaldisc, which increases a jitter component and an error rate.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aninformation reproducing apparatus for and an information reproducingmethod of decreasing the error rate in the reproduction of data recordedby the wobble, as one example.

The above object of the present invention can be achieved by aninformation reproducing apparatus for reproducing information recordedon an information recording medium, on which a record mark having avariable length according to first data is formed at a displacedposition to which the record mark is displaced in a direction crossing areading direction of the record mark according to a wobble signalobtained by modulating second data in a predetermined modulating method,the information reproducing apparatus comprising: a reading device forreading the record mark recorded on the information recording medium; aread signal generating device for generating a read signal forindicating the length of the record mark on the basis of an outputsignal from the reading device; a first clock signal generating devicefor generating a first clock signal on the basis of the read signal; awobble signal generating device for generating a wobble signal forindicating the displaced position of the read mark on the basis of theoutput signal from the reading device; and a second data reproducingdevice for reproducing the second data from the generated wobble signalby using the first clock signal.

The above object of the present invention can be also achieved by aninformation reproducing method of reproducing information recorded on aninformation recording medium, on which a record mark having a variablelength according to first data is formed at a displaced position towhich the record mark is displaced in a direction crossing a readingdirection of the record mark according to a wobble signal obtained bymodulating second data in a predetermined modulating method, theinformation reproducing method comprising: a reading process of readingthe record mark recorded on the information recording medium; a readsignal generating process of generating a read signal for indicating thelength of the record mark on the basis of an output signal read by thereading process; a first clock signal generating process of generating afirst clock signal on the basis of the read signal; a wobble signalgenerating process of generating a wobble signal for indicating thedisplaced position of the read mark on the basis of the output signalread by the reading process; and a second data reproducing process ofreproducing the second data from the generated wobble signal by usingthe first clock signal.

The nature, utility, and further features of this invention will be moreclearly apparent from the following detailed description with referenceto preferred embodiments of the invention when read in conjunction withthe accompanying drawings briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the outline structure of aninformation reproducing apparatus associated with an embodiment of thepresent invention;

FIG. 2 is a block diagram showing the structure of an informationreproducing apparatus associated with an example of the presentinvention;

FIG. 3 is a block diagram showing the structure of a pit data generationcircuit 11 used for the apparatus;

FIG. 4 is a timing chart showing the relationship among a wobble signalWB, a binary signal 24 a, a first clock signal CK1, a second clocksignal CK2, and a pit synchronization signal SYNC; and

FIG. 5 is a timing chart showing the relationship among spread spectrumdata SS, random data RND, and second data D2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention will be explained withreference to one of the drawings hereinafter. FIG. 1 shows the mainportion of an information reproducing apparatus associated with anembodiment of the present invention. This information reproducingapparatus 100 reproduces an information recording medium A thereon. Theinformation recording medium A is disc-shaped and can adopt variousoptical discs, such as a CD, a Compact Disc-Read Only Memory (CD-ROM), aDVD, and a DVD-ROM.

On the information recording medium A, record marks are formed alongcircular tracks as pits P. First data D1 is recorded according to thevariable length (i.e., the long or short length) of the record mark. Thetrack, in close-up, meanders or wobbles in the direction crossing areading direction. This meandering or wobbling of the track is referredto as the “wobble” and has a shape corresponding to a wobble signal WB.The wobble signal WB is obtained by modulating second data D2 in apredetermined modulating method. In other words, the record mark isformed at a position displaced in the direction crossing the readingdirection according to the wobble signal WB. The embodiment adopts aspread spectrum modulating method as the predetermined modulatingmethod. Incidentally, the first data D1 is synchronized with the seconddata D2 upon recording. Moreover, the first data D1 is synchronized withthe wobble signal WB.

The information reproducing apparatus 100 is provided with: a readingdevice E; a read signal generating device F; a wobble signal generatingdevice G; a first data reproducing device B; a second data reproducingdevice C; and a first clock signal generating device D. The readingdevice E reads the record mark recorded on the information recordingmedium A. The read signal generating device F generates a read signal RFfor indicating the long or short length of the record mark on the basisof an output signal from the reading device E. The first clock signalgenerating device D generates a first clock signal DK1 from the readsignal RF. The read signal RF is a signal obtained by reading the longor short length of the record mark recorded on the information recordingmedium A. The minimum reverse interval of the first data D1 is M timesas long as one cycle of the first clock signal CK1.

The wobble signal generating device G generates the wobble signal WB forindicating the displaced position of the read mark on the basis of theoutput signal from the reading device E. The first data reproducingdevice B reproduces the first data D1 from the read signal RF by usingthe first clock signal CK1. The second data reproducing device Creproduces the second data D2 by performing predetermined processingusing the first clock signal CK1 with respect to the generated wobblesignal WB. Namely, it generates the second data D2 from the wobblesignal WB by using the first clock signal CK1 reproduced from the longor short length of the record mark. In the reproduction of digitalinformation, it is general to generate a clock signal from a wobblesignal. Therefore, it is conceivable to reproduce a clock signal forextracting the second data D2 from the reproduced wobble signal WB.

However, providing a reproduction circuit independently of the firstclock signal generating device D makes the structure complicated.Moreover, since the wobble signal WB determines the meandering orwobbling of the track, the frequency thereof is lower than that of therecord mark. On the other hand, the read signal RF and the wobble signalWB are generated by rotating the disc-shaped information recordingmedium A upon reproducing. Ideally, it is desirable that there is noeccentricity on the information recording medium A, but actually thereis eccentricity to some extent on the information recording medium A.Thus, the read signal RF and the wobble signal WB are influenced by theeccentricity, causing jitter. The wobble signal WB is easily influencedby the jitter because of its low frequency, but the read signal RF has ashorter period and a smaller jitter amount because of its highfrequency, which increases accuracy as a sampling clock. That is why thesecond data D2 is generated from the wobble signal WB by using the firstclock signal CK1 extracted from the read signal RF. This allows thesimplified structure of the information reproducing apparatus 100 and atthe same time allows the reproduction of the second data D2 withoutalmost any influence of the eccentricity, thereby drastically improvingthe error rate of the second data D2.

The second data reproducing device C is provided with: a random datagenerating device C1; a second clock signal generating device C2; and areproducing device C3. The random data generating device C1 is providedwith a non-volatile memory or the like in which random data RND used forthe spread spectrum of the second data D2 is stored. The second clocksignal generating device C2 generates a second clock signal CK2synchronized with the first clock signal CK1. The second clock signalgenerating device C2 may have any structure if capable of generating thesecond clock signal CK2 on the basis of the first clock signal CK1, andmay be a Phase Locked Loop (PLL) circuit and a division circuit (e.g., afrequency division circuit), for example. In particular, if thefrequency of the first clock signal CK1 is an integral multiple of thefrequency of the second clock signal CK2, the division circuit ispreferably used from the viewpoint of the simplified structure, and ifnot, the PLL circuit is preferably used.

The reproducing device C3 reads the random data RND from the random datagenerating device C1 by using the second clock signal CK2 and reproducesthe second data D2 by demodulating the reproduced wobble signal WB onthe basis of the read random data RND. Thus, the random data RND is readby using the second clock signal CK2 synchronized with the first clocksignal CK1.

Moreover, the reproducing device C3 is provided with a sampling deviceC31 and a demodulating device C32. The sampling device C31 samples thereproduced wobble signal WB with the second clock signal CK2. Thedemodulating device C32 reproduces the second data D2 by performing aninverse-spread spectrum (i.e., performing a back-spread orreverse-spread spectrum) with respect to the spread spectrum data SSoutputted from the sampling device C31, on the basis of the random dataRND read from the random data generating device C1 by using the secondclock signal CK2.

Since the wobble signal WB has a lower frequency than that of the readsignal RF, the inclination of the wobble signal WB near zero crossing isrelatively mild. Therefore, if the wobble signal WB is only binarized bya comparator or the like, the jitter amount is large. In the embodiment,the spread spectrum data SS is extracted by sampling the wobble signalWB with the second clock signal CK2. The spread spectrum data SS isobtained by performing the spread spectrum with respect to the seconddata D2. Since the second clock signal CK2 is generated from the firstclock signal CK2 having the high frequency, it is possible to accuratelyadjust the phase of the second clock signal CK2 with the cycle of thefirst clock signal CK1. For example, if the spread spectrum data SS isextracted at the trailing or falling edge of the second clock signalCK2, the spread spectrum data SS may accurately be extracted from thewobble signal WB by adjusting a timing so as to set the trailing edge ofthe second clock signal CK2 to the center of the data reverse interval(which is the interval while the data is reverted or inverted) of thewobble signal WB.

More specifically, if the data rate of the first data D1 is N times (N:natural number, N≧2) as large as that of the random data RND, the secondclock signal generating device C2 is preferably provided with afrequency-division circuit for 1/N-frequency-dividing the first clocksignal CK1 (i.e., for dividing the frequency of the first clock signalCK1 by N, to thereby generate a lower frequency clock as the secondclock signal CK2). Moreover, the first data reproducing device Bpreferably outputs a particular signal obtained by extracting aparticular data pattern included in the first data D1, and the divisioncircuit is preferably reset by the particular signal or a signalobtained by delaying the particular signal by a predetermined timelength. In this case, the particular signal may be the synchronizationsignal SYNC of the first data D1.

EXAMPLE

Next, the preferred example of the preset invention will be explainedwith reference to the drawings. FIG. 2 shows the structure of theinformation reproducing apparatus 100. On an optical disc 1, pit data DPsynchronized with the first clock signal CK1 is recorded by the length(i.e., the long or short length) of the record mark. The record mark inthis example is a pit, and the track is constructed from a pit row. Thetrack has a meandering or wobbling shape corresponding to the wobblesignal WB obtained by the spread spectrum modulation of the second dataD2. The wobble signal WB is synchronized with the second clock signalCK2. The first clock signal CK1 has a frequency N times (N: naturalnumber) as large as that of the second clock signal CK2. In thisexample, N=250, the frequency of the second clock signal CK2 is 420 KHz,and the frequency of the first clock signal CK1 is 10.5 MHz. The pitdata DP corresponds to the first data D1 described above, and theoptical disc 1 corresponds to the information recording medium A.

The information reproducing apparatus 100 is provided with: an opticalpickup 2 for irradiating a reproduction beam onto the optical disc 1 andfor outputting a signal corresponding to reflected light; a spindlemotor 3 for controlling the rotation of the optical disc 1; and a servounit 22. The first clock signal CK1 and the pit synchronization signalSYNC are supplied to the servo unit 22. In synchronization with thesesignals, the servo unit 22 performs spindle servo for controlling therotation of the spindle motor 3 and focus servo and tracking servo forcontrolling the relative position of the optical pickup 2 with respectto the optical disc 1.

The optical pickup 2 is provided with: a laser diode for irradiating thereproduction beam; and a four-division detection circuit(not-illustrated). The four-division detection circuit divides by 4 thereflected light of the reproduction beam into areas 1A, 1B, 1C, and 1Dshown in FIG. 2, and outputs each signal corresponding to the quantityof light in respective one of the areas. A head amplifier 4 amplifieseach output signal of the optical pickup 2, and outputs a divisionalread signal 1 a corresponding to the area 1A, a divisional read signal 1b corresponding to the area 1B, a divisional read signal 1 ccorresponding to the area 1C, and a divisional read signal 1 dcorresponding to the area 1D. The optical pickup 2 and the headamplifier 4 correspond to the reading device E described above.

A sum generation circuit 10 corresponds to the read signal generatingdevice F and is constructed from an addition circuit for adding thedivisional read signals 1 a, 1 b, 1 c, and 1 d and for outputting a sumread signal SRF. Incidentally, the sum read signal SRF represents thelength (i.e., the long or short length) of the record mark andcorresponds to the read signal RF described above.

A pit data generation circuit 11 reproduces the pit data DP andgenerates the first clock signal CK1 on the basis of the sum read signalSRF. The pit data generation circuit 11 corresponds to the first datareproducing device B and the first clock signal generating device Ddescribed above. FIG. 3 shows the structure of the pit data generationcircuit 11. As shown in FIG. 3, the pit data generation circuit 11 isprovided with: a first clock signal reproduction circuit 111; a pit dataextraction circuit 112; a synchronization signal detection circuit 113;a pit data demodulation circuit 114; and a descrambler circuit 115.

The first clock signal reproduction circuit 111 reproduces the firstclock signal CK1 synchronized with the pit data DP on the basis of thesum read signal SRF. The pit data extraction circuit 112 samples, withthe first clock signal CK1, a binary signal obtained by binarizing thesum read signal SRF and reproduces the pit data DP.

The synchronization signal detection circuit 113 detects asynchronization pattern included in the reproduced pit data DP andgenerates the pit synchronization signal SYNC. The synchronizationpattern is a particular data pattern which is not included in other pitdata, and has a constant cycle. The pit synchronization signal SYNCindicates the timing of the synchronization pattern. Incidentally, thepit synchronization signal SYNC in this example is active (at a lowlevel) only in one cycle of the first clock signal CK1 from thebeginning of the synchronization pattern.

The pit data demodulation circuit 114 generates reproduction data bydemodulating the reproduced pit data DP with a predetermined table, withthe pit synchronization signal SYNC being as a reference position. Forexample, if Eight to Fourteen Modulation (EFM) is used as a modulatingmethod, the demodulation processing is performed in which 14 bits of thepit data DP is converted into 8 bits of the reproduction data. Thedescrambler circuit 115 performs descrambling in which the order of thereproduction data is rearranged according to a preset rule, and outputsthe processed reproduction data.

The reproduction data as obtained above is supplied to a pit data errorcorrection circuit 12 shown in FIG. 2, and after error correcting andinterpolating therein, it is stored into a buffer 13. An interface 14sequentially reads the data stored in the buffer 13, converts it into apredetermined output form, and outputs it to external equipment.

Back in FIG. 2, the explanation goes on. A push-pull signal generationcircuit 20 calculates (1 a+1 d)−(1 b+1 c) and generates a push-pullsignal. The component (1 a+1 d) corresponds to the areas 1A and 1D whichare on the left side with respect to the reading direction, while thecomponent (1 b+1 c) corresponds to the areas 1B and 1C which are on theright side with respect to the reading direction. Namely, if thereproduction beam inclines to the left side with respect to the pit, thepush-pull signal will have positive polarity with the amplitude centerthereof as a standard. If the reproduction beam is positioned in thecenter of the pit, the value of the push-pull signal will be in theamplitude center thereof. If the reproduction beam inclines to the rightside with respect to the pit, the push-pull signal will have negativepolarity with the amplitude center thereof as a standard. The relativeposition between the reproduction beam and the pit changes according tothe meandering of the track, and the value of the push-pull signalrepresents the relative position between the reproduction beam and thepit. Namely, the push-pull signal is a signal corresponding to themeandering of the track.

The push-pull signal is outputted through a low pass filter 21 to theservo unit 22. The servo unit 22 performs tracking control on the basisof the push-pull signal. Moreover, the push-pull signal is supplied to aband pass filter 23. The pass band of the band pass filter 23 is set toextract the wobble signal WB obtained by the spread spectrum modulationof the second data D2 upon recording from the push-pull signal.Therefore, the band pass filter 23 constitutes the wobble signalgenerating device G described above with the push-pull signal generationcircuit 20, and the output signal thereof is such as to reproduce thewobble signal WB from the optical disc 1.

FIG. 4 shows the relationship among the wobble signal WB, a binarysignal 24 a, the first clock signal CK1, the second clock signal CK2,and the pit synchronization signal SYNC. The comparator 24 outputs thebinary signal 24 a obtained by binarizing the wobble signal WB. Sincethe wobble signal WB has a low frequency, the inclination thereof nearzero crossing is relatively mild. Thus, the binary signal 24 a has alarge jitter component. The sampling circuit 25 samples the binarysignal 24 a by using the second clock signal CK2 and reproduces thespread spectrum data SS by extracting the data.

In this example, the frequency f1 of the first clock signal CK1 is 10.5MHz and the frequency f2 of the second clock signal CK2 is 420 KHz. Thefirst clock signal CK1 has a frequency 250 times as large as that of thesecond clock signal CK2. Thus, the division circuit 26 generates thesecond clock signal CK2 by frequency-dividing the first clock signal CK1by 250. Therefore, as shown in FIG. 4, one cycle of the second clocksignal CK2 can contain therein 250 first clock signals CK1. The divisioncircuit 26 is set to be reset if the voltage of a reset terminal R isactive (at a low level), and the pit synchronization signal SYNC issupplied to the reset terminal R. Therefore, the second clock signal CK2is reset by the trailing edge of the pit synchronization signal SYNC,and its phase is determined from the pit synchronization signal SYNC.

The synchronization patterns are inserted in the pit data DP with aperiod of 250*K (K: natural number) bits, and each has such arelationship that the beginning of the synchronization pattern agreeswith the leading or rising edge of the second clock signal CK2. Namely,the synchronization pattern has a frequency which is a natural multipleof that of the second clock signal CK2. In this case, if the pitsynchronization signal SYNC becomes active at the timing shown in FIG.4, the division circuit 26 is reset and the phases of the pitsynchronization signal SYNC and the second clock signal CK2 areadjusted. This makes it possible to set the trailing edge of the secondclock signal CK2 to the center of the data minimum reverse interval ofthe binary signal 24 a. Therefore, even if the edge of the binary signal24 a is influenced and wobbled by jitter, it is possible to certainlyextract the spread spectrum data SS.

Back in FIG. 2, the explanation goes on. A random pattern used for thespread spectrum modulation upon recording is stored on a RAND table 27.The random pattern corresponds to a spread code and is a bit rowgenerated by using a random function. The second clock signal CK2 issupplied to the RAND table 27. By reading the random pattern insynchronization with the second clock signal CK2, the random data RND isgenerated. The generated random data RND is supplied to a spreadspectrum data demodulation circuit 28. Moreover, the spread spectrumdata SS outputted from the sampling circuit 25 is also supplied to thespread spectrum data demodulation circuit 28. Incidentally, the divisioncircuit 26 corresponds to the second clock signal generating device C2.The comparator 24 and the sampling circuit 25 correspond to the samplingdevice C31. The spread spectrum data demodulation circuit 28 correspondsto the demodulating device C32. The RAND table 27 corresponds to therandom data generating device C1.

FIG. 5 shows the relationship among the spread spectrum data SS, therandom data RND, and the second data D2. The spread spectrum datademodulation circuit 28 is constructed from a multiplication circuit(e.g. an exclusive OR (XOR) circuit) and reproduces the second data D2by multiplying the spread spectrum data SS and the random data RND. Inthis case, a signal which is not in an original signal band is convertedinto a signal which is out of the band by the multiplication. The seconddata D2 reproduced in this manner is outputted after error correcting onthe error correction circuit 29.

The present invention is not limited to the above-described example andcan adopt the following modification, for example. In the above example,the sampling circuit 25 samples the binary signal 24 a with the secondclock signal CK2 and reproduces the spread spectrum data SS, but insteadof the second clock signal CK2, the first clock signal CK1 may be usedfor the sampling, and data after the sampling may be corrected. In thiscase, the sampling circuit 25 may supply the data after the sampling tothe spread spectrum data demodulation circuit, demodulate the spreadspectrum, and then correct it by using the second clock signal CK2 orthe like. The point is any method may be used if the second data D2 isreproduced by performing predetermined processing using the first clocksignal CK1 with respect to the wobble signal WB reproduced from theoptical disc 1 as being the information recording medium A.

Moreover, when the second data D2 with respect to which the spreadspectrum is performed is recorded onto the information recording mediumA, it is also possible to prepare a plurality of random patterns, selectone of the plurality of random patterns according to a predeterminedrule, generate the wobble signal WB by the spread spectrum modulation ofthe second data D2 by using the selected random pattern, and form therecord mark at a displaced position, to which it is displaced in thedirection crossing the reading direction according to the generatedwobble signal WB. If the second data D2 is reproduced from such aninformation recording medium A, what is needed is to prepare a pluralityof RAND tables 27 and demodulate the spread spectrum data SS by usingthe random data RND selectively read from the RAND tables 27 accordingto a predetermined rule.

Moreover, in the above example, the case where the beginning of thesynchronization pattern of the pit data DP agrees with the timing of theleading edge of the second clock signal CK2 is explained as one example.If the synchronization pattern of the pit data DP does not agree withthe timing of the trailing edge of the second clock signal CK2 only by apredetermined number of the first clock signals CK1, the divisioncircuit 26 may be reset in the following manner. Namely, if the pitsynchronization signal SYNC becomes active, a counter for starting tocount the first clock signals CK1 and a comparison circuit for comparingthe counted value of the counter with the predetermined number may beprovided, and the division circuit 26 may be reset at a timing at whichthe agreement is detected on the comparison circuit. In this case, thedivision circuit 26 is reset by a signal obtained by delaying the pitsynchronization signal SYNC by a predetermined time length.

The present invention may be such as to extract a particular datapattern from the pit data DP and adjust the phase of the second clocksignal CK2 on the basis of a particular signal (synchronization signal)extracted upon reproducing, and is preferably such as to adjust it bythe unit of one period of the first clock signal CK1.

As explained above, according to the above example and modified example,if the second data D2 is reproduced from the information recordingmedium A on which the pit data DP is recorded according to the length(i.e., the long or short length) of the record mark and on which therecord mark is formed at a displaced position to which it is displacedin the direction crossing the reading direction according to the wobblesignal WB obtained by the modulation of the second data D2 in apredetermined modulating method, the first clock signal CK1 synchronizedwith the pit data DP is reproduced from a signal obtained by reading thelong or short length of the record mark and this first clock signal CK1is used to reproduce the second data D2. Therefore, it is possible tomake it unnecessary to generate the second clock signal CK2 from thereproduced wobble signal WB and at the same time it is possible toaccurately extract the spread spectrum data SS, and thus it is possibleto drastically decrease the error rate of the second data D2.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

The entire disclosure of Japanese Patent Application No. 2003-147941filed on May 26, 2003 including the specification, claims, drawings andsummary is incorporated herein by reference in its entirety.

1-9. (canceled)
 10. An information reproducing apparatus for reproducinginformation recorded on an information recording medium, on which arecord mark having a variable length according to first data is formedat a displaced position to which the record mark is displaced in adirection crossing a reading direction of the record mark according to awobble signal obtained by modulating second data in a predeterminedmodulating method, said information reproducing apparatus comprising: areading device for reading the record mark recorded on said informationrecording medium; a read signal generating device for generating a readsignal for indicating the length of the record mark on the basis of anoutput signal from said reading device; a first clock signal generatingdevice for generating a first clock signal on the basis of the readsignal; a wobble signal generating device for generating a wobble signalfor indicating the displaced position of the read mark on the basis ofthe output signal from said reading device; a first data reproducingdevice for reproducing the first data from the read signal by using thefirst clock signal, and for outputting a synchronization signal obtainedby extracting a synchronization pattern included in the reproduced firstdata; and a second data reproducing device for reproducing the seconddata from the generated wobble signal by using the first clock signal,said second data reproducing device comprising: a second clock signalgenerating device for generating a second clock signal synchronized withthe first clock signal; and a delaying device for delaying thesynchronization signal by a predetermined time length, the first dataand the second data being recorded on the information recording mediumsuch that the synchronization pattern does not agree with a timing of atrailing edge of said second clock signal by a predetermined number. 11.The information reproducing apparatus according to claim 10, whereinsaid second clock signal generating device includes a division circuitfor 1/N-frequency dividing the first clock signal, the frequencydivision circuit is reset by the delayed synchronization signal.
 12. Theinformation reproducing apparatus according to claim 10, wherein thepredetermined modulating method is a spread spectrum method.
 13. Theinformation reproducing apparatus according to claim 10, wherein saiddelaying device comprises: a counting device for starting to count saidfirst clock signal if the synchronization signal is detected; and acomparison circuit for comparing a counted value of said counting devicewith the predetermined number, the predetermined time length is a lengthof time from when said counting device starts to count until when saidcomparison circuit detects an agreement between the counted value andthe predetermined number.
 14. An information reproducing method ofreproducing information recorded on an information recording medium, onwhich a record mark having a variable length according to first data isformed at a displaced position to which the record mark is displaced ina direction crossing a reading direction of the record mark according toa wobble signal obtained by modulating second data in a predeterminedmodulating method, said information reproducing method comprising: areading process of reading the record mark recorded on said informationrecording medium; a read signal generating process of generating a readsignal for indicating the length of the record mark on the basis of anoutput signal from said reading process; a first clock signal generatingprocess of generating a first clock signal on the basis of the readsignal; a wobble signal generating process of generating a wobble signalfor indicating the displaced position of the read mark on the basis ofthe output signal from said reading process; a first data reproducingprocess of reproducing the first data from the read signal by using thefirst clock signal, and for outputting a synchronization signal obtainedby extracting a synchronization pattern included in the reproduced firstdata; and a second data producing process of reproducing the second datafrom the generated wobble signal by using the first clock signal, saidsecond data reproducing process comprising: a second clock signalgenerating process of generating a second clock signal synchronized withthe first clock signal; and a delaying process of delaying thesynchronization signal by a predetermined time length, the first dataand the second data being recorded on the information recording mediumsuch that the synchronization pattern does not agree with a timing of atrailing edge of said second clock signal by a predetermined number.